Electrical components and method for the fabrication thereof

ABSTRACT

This invention relates to a primer that improves adherence of a cured resin sealant to a cured silicone coating on an electrical element, wherein said primer is selected from the group consisting of: 
     (i) a mixture of components (a) and (b), 
     (ii) a reaction mixture of components (a) and (b), 
     (iii) component (c), 
     (iv) component (c) and a mixture of components (a) and (b), and 
     (v) component (c) and a reaction mixture of components (a) and (b), 
     where component (a) is silanol-functional organopolysiloxane; component (b) is epoxy-functional organoalkoxysilane; and component (c) is organopolysiloxane with the average unit formula: (R 1  SiO 3/2 ) a  (R 2   2  SiO 2/2 ) b  (R 2   3  SiO 1/2 ) c  (R 3  O 1/2 ) d   
     where R 1  is an epoxy-functional monovalent organic group; each R 2  is independently a monovalent hydrocarbon group, R 3  is selected from the group consisting of hydrogen and alkyl groups of 1 to 4 carbon atoms; a, b, and d are each a positive number; and c is 0 or a positive number.

This application is a divisional of application Ser. No. 08/923,074filed on Sep. 3, 1997, now U.S. Pat. No. 5,958,515.

BACKGROUND OF THE INVENTION

This invention relates to electrical components and methods for theirfabrication. More particularly, the invention relates to highly reliableelectrical components in which cured silicone coated on an electricalelement has been thoroughly monolithically adhered with cured resinsealant coated on the cured silicone. The invention also relates to ahighly productive method for fabricating the electrical components.

Electrical elements, e.g., integrated circuits, hybrid integratedcircuits, semiconductor chips, transistors, diodes, capacitors,resistors, etc., are generally coated with a cured resin sealant. Thesealant protects the element from external stresses (flexural stresses,impact, etc.), prevents water infiltration, and improve moisturesresistance. In addition, the electrical element may also be coated withcured silicone to protect it from internal stresses originating from theexpansion and shrinkage of the cured resin sealant. However, the curedsilicone does not bond or adhere to the over-coated cured resin sealant,which results in unacceptable reliability for the resin-sealedelectrical component.

To date, monolithic bonding between the cured silicone coating theelectrical element and the cured sealant resin over-coating the curedsilicone has been pursued by treating the surface of the cured siliconewith ultraviolet radiation and sealing this UV-treated cured siliconewith the resin sealant (U.S. Pat. No. 4,645,551, JP-A 64-27249, JP-A1-94679, JP-A 2-27756, and JP-A 3-22553).

However, even electrical components of this type suffer from anunacceptable adherence between the cured silicone and the cured resinsealant. As a result, the reliability of these resin-sealed electricalcomponents remains unsatisfactory. Moreover, the methods for fabricatingthese electrical components suffer from poor productivity because theyrequire irradiation with ultraviolet light.

Therefore, an object of the present invention is to provide highlyreliable electrical components with the cured silicone coating theelectrical element thoroughly bonded into a monolithic mass with thecured resin sealant coated on the cured silicone. A further object ofthis invention is to provide a highly productive method for thefabrication of the electrical components.

SUMMARY OF THE INVENTION

The primer of the present invention is selected from the groupconsisting of:

(i) a mixture of components (a) and (b),

(ii) a reaction mixture of components (a) and (b),

(iii) component (c),

(iv) component (c) and a mixture of components (a) and (b), and

(v) component (c) and a reaction mixture of components (a) and (b),

where component (a) is silanol-functional organopolysiloxane; component(b) is epoxy-functional organoalkoxysilane; and component (c) isorganopolysiloxane with the average unit formula: (R¹ SiO_(3/2))_(a) (R²₂ SiO_(2/2))_(b) (R² ₃ SiO_(1/2))_(c) (R³ O_(1/2))_(d)

where R¹ is an epoxy-functional monovalent organic group; each R² isindependently a monovalent hydrocarbon group, R³ is selected from thegroup consisting of hydrogen and alkyl groups of 1 to 4 carbon atoms; a,b, and d are each a positive number; and c is 0 or a positive number.

The fabrication method for electrical components of the presentinvention comprises:

(A) treating the surface of the cured silicone coated on an electricalelement with the primer of this invention, and

(B) sealing the treated cured silicone with a resin sealant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 contains a cross section of a semiconductor device provided as anelectrical component according to the present invention.

FIG. 2 contains an oblique view with partial cut-away of a capacitorprovided as an electrical component according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The electrical components of the present invention have the curedsilicone coated on an electrical element thoroughly adhered into amonolith with the cured resin sealant over-coated on the cured silicone.The cured silicone under consideration is not critical and may take theform, for example, of a gel, rubber, or hard resin. The compositionsgiving this cured silicone can be, for example, addition reaction-curingsilicone compositions or condensation reaction-curing siliconecompositions. Addition reaction-curing silicone compositions arepreferred, while addition reaction-curing silicone compositions thatgenerate silicone rubbers are particularly preferred. Additionreaction-curing silicone compositions of this type are exemplified bycompositions comprising organopolysiloxane having at least 2 alkenylgroups per molecule, organopolysiloxane having at least 2 silicon-bondedhydrogen atoms per molecule, and platinum catalyst.

Cured resin sealants generally are relatively poorly adhesive to thecured products. The sealants are particularly poorly adhesive to thesilicone rubbers afforded by the cure of addition reaction-curingsilicone compositions comprising organopolysiloxane having at least 2alkenyl groups per molecule, organopolysiloxane having at least twosilicon-bonded hydrogen atoms per molecule, and platinum catalyst.However, these addition reaction-cured silicones are still preferablyused as the cured silicone because, in an electrical component of thepresent invention, they become thoroughly adhered into a monolithic masswith the cured resin sealant over-coated on the cured silicone.

Adherence between the cured silicone coating and cured resin sealant isimproved by this invention by treating the surface of the coating with aprimer. The primer of the present invention is selected from the groupconsisting of:

(i) a mixture of components (a) and (b),

(ii) a reaction mixture of components (a) and (b),

(iii) component (c),

(iv) component (c) and a mixture of components (a) and (b), and

(v) component (c) and a reaction mixture of components (a) and (b),

where component (a) is silanol-functional organopolysiloxane; component(b) is epoxy-functional organoalkoxysilane; and component (c) isorganopolysiloxane with the average unit formula: (R¹ SiO_(3/2))_(a) (R²₂ SiO_(2/2))_(b) (R² ₃ SiO_(1/2))_(c) (R³ O_(1/2))_(d)

where R¹ is an epoxy-functional monovalent organic group; each R² isindependently a monovalent hydrocarbon group, R³ is selected from thegroup consisting of hydrogen and alkyl groups of 1 to 4 carbon atoms; a,b, and d are each a positive number; and c is 0 or a positive number.

Silanol-functional organopolysiloxane (a) contains the silanol group,i.e., the silicon-bonded hydroxyl group. Particularly preferred isorganopolysiloxane that contains at least 2 silanol groups per molecule.The molecular chain structure of component (a) can be, for example,straight, partially branched straight, branched, cyclic, or network.Straight-chain molecular structures are preferred.

The silicon-bonded organic groups in component (a) are exemplified bysubstituted and unsubstituted monovalent hydrocarbon groups, e.g., byalkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl,heptyl, and so forth; alkenyl groups such as vinyl, allyl, butenyl,pentenyl, hexenyl, heptenyl, and so forth; aryl groups such as phenyl,tolyl, xylyl, naphthyl, and so forth; aralkyl groups such as benzyl,phenethyl, and so forth; and halogenated alkyl groups such aschloromethyl, 3-chloropropyl, 3,3,3-trifluoropropyl, and so forth.Methyl, vinyl, and phenyl are particularly preferred.

Component (a) is specifically exemplified by silanol-endblockeddimethylpolysiloxanes, silanol-endblockeddimethylsiloxane-methylvinylsiloxane copolymers, and silanol-endblockeddimethylsiloxane-methylphenylsiloxane copolymers. The viscosity ofcomponent (a) at 25° C. is, for example, preferably from 1 to 500 mPa s,more preferably from 1 to 200 mPa s, and particularly preferably from 1to 100 mPa s because such values afford substantial effects from theprimer treatment.

Epoxy-functional organoalkoxysilane (b) contains the epoxy group and isexemplified by organoalkoxysilane with the general formula R¹ Si(OR⁴)₃.R¹ represents epoxy-functional monovalent organic groups, for example,glycidoxyalkyl groups such as 3-glycidoxypropyl, 4-glycidoxybutyl, andso forth; epoxycyclohexylalkyl groups such as2-(3,4-epoxycylohexyl)ethyl, 3-(3,4-epoxycyclohexyl)propyl, and soforth; and oxiranylalkyl groups such as 4-oxiranylbutyl,8-oxiranyloctyl, and so forth. Glycidoxyalkyl groups such as3-glycidoxypropyl and so forth are specifically preferred here. R⁴formula represents alkyl groups of 1 to 4 carbon atoms, for example,methyl, ethyl, propyl, and butyl, wherein methyl is specificallypreferred.

Component (b) is specifically exemplified by3-glycidoxypropyltrimethoxysilane,2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,4-oxiranylbutyltrimethoxysilane, and 8-oxiranyloctyltrimethoxysilanewherein 3-glycidoxypropyltrimethoxysilane is particularly preferred.

Components (a) and (b) may simply be mixed or may be subjected tocondensation and equilibration reactions. The component (a): component(b) mixing ratio or reaction ratio is preferably from 1:99 to 99:1 byweight.

Organopolysiloxane (c) is represented by the following average unitformula:

    (R.sup.1 SiO.sub.3/2).sub.a (R.sup.2.sub.2 SiO.sub.2/2).sub.b (R.sup.2.sub.3 SiO.sub.1/2).sub.c (R.sup.3 O.sub.1/2).sub.d

where R¹, R², R³, a, b, c, and d are defined above. Glycidoxyalkylgroups, such as 3-glycidoxypropyl and so forth, are specificallypreferred for R¹.

R² is exemplified by substituted and unsubstituted monovalenthydrocarbon groups as exemplified by alkyl such as methyl, ethyl,propyl, butyl, and so forth; alkenyl such as vinyl, allyl, butenyl,pentenyl, hexenyl, and so forth; aryl such as phenyl, tolyl, xylyl, andso forth; aralkyl such as benzyl, phenethyl, and so forth; andhalogenated alkyl groups such as 3,3,3-trifluoropropyl and so forth.Methyl, vinyl, and phenyl are specifically preferred for R².

R³ is exemplified by methyl, ethyl, propyl, and butyl.

The viscosity of component (c) at 25° C. is, for example, preferablyfrom 1 to 500 mPa s, more preferably from 1 to 200 mPa s, andparticularly preferably from 1 to 100 mPa s because such values affordsubstantial effects from the primer treatment.

Component (c) can be synthesized, for example, by an equilibrationpolymerization in the presence of a polymerization catalyst, e.g.,potassium hydroxide, etc., between epoxy-functional alkoxysilane andstraight chain-to-cyclic diorganosiloxane.

The primer treated cured silicone is sealed with a cured resin sealant.The resin sealant is not critical and can be, for example, the curedproduct from curable epoxy, phenolic, polyphenylene sulfide,polyetheramide, and polyimide resins. Curable epoxy resins areparticularly preferred.

The curable epoxy resins are exemplified by the glycidyl ether epoxyresins, for example, bisphenol A-type, bisphenol F-type, biphenyl,phenol novolac, ortho-cresol novolac, brominated, and so forth;alicyclic epoxy resins; glycidyl ester epoxy resins; glycidyl amineepoxy resins; and heterocyclic epoxy resins. The cure mechanisms inthese curable epoxy resins can be, for example, heat-curing, UV-curing,or moisture curing, wherein heat-curing mechanisms are specificallypreferred. Moreover, while the curable epoxy resin can be a liquid atroom temperature or can be a solid having a softening point of at leastroom temperature, curable epoxy resins that are liquid at roomtemperature are preferred for their good handling properties.

The electrical component of the present invention can be, for example, atransistor, diode, capacitor, or resistor or a semiconductor device thatcontains an electrical element such as a semiconductor element (e.g.,integrated circuit, hybrid integrated circuit, computer chip, and soforth), transistor, diode, capacitor, resistor, and so forth.Semiconductor devices and capacitors are specifically preferred for theelectrical component. An example of a semiconductor device is providedin FIG. 1, while FIG. 2 contains an example of a capacitor.

The semiconductor device in FIG. 1 is herein described in detail. Asemiconductor element 3 is mounted in this semiconductor device on acircuit substrate 1 through an interposed adhesive 2. The upper edges ofthis semiconductor element 3 are provided with bonding pads 4, whileouter leads 5 are provided at the edges of the circuit substrate 1. Thebonding pads 4 are electrically connected to the circuit substrate 1 bybonding wires 6. The semiconductor element 3 is coated with curedsilicone 7, and a primer-treated layer 8, of the composition describedabove, has been formed on the surface of this cured silicone 7. Curedresin sealant 9 is coated over the cured silicone. In order to preventoutflow of the sealant resin, a frame or dam 10 is provided around theperiphery of the semiconductor element 3. The cured silicone 7 isthoroughly bonded into a monolith with the over-coated cured resinsealant 9 through the interposed primer-treated layer 8 formed on thesurface of the cured silicone 7.

The capacitor, FIG. 2, contains Al-vapor-deposited (metallized)polyester film 11 in either a rolled or layered configuration, andelectrodes 12 are provided by coating both ends with flame-coated metal.These electrodes 12 are electrically connected with outer leads 13. Thecapacitor is coated with cured silicone 14, while a primer-treated layer15, of the composition described above, has been formed on the surfaceof this cured silicone 14. Cured resin sealant 16 is coated over thecured silicone. The cured silicone 14 is thoroughly bonded into amonolith with the over-coated cured resin sealant 16 through theinterposed primer-treated layer 15 formed on the surface of the curedsilicone 14.

The method for fabricating the electrical components of the presentinvention is described in detail as follows. Before fabricating thesemiconductor device of FIG. 1, first the semiconductor device 3 must bemounted on the circuit substrate 1 using interposed adhesive 2 and thebonding pads 4 on the upper edges of this semiconductor device 3 must beelectrically connected with the circuit substrate 1 by bonding wires 6.In addition, when the resin sealant is fluid, a dam or frame 10 ispreferably provided around the periphery of the semiconductor element 3in order to inhibit outflow of the resin sealant.

Before fabricating the capacitor of FIG. 2 as the electrical component,first the Al-vapor-deposited (metallized) polyester film 11 must berolled up or laminated, the electrodes 12 must be formed by coating bothends with flame-coated metal, and the outer leads 13 must beelectrically connected to the electrodes 12.

The method for coating the cured silicone onto electrical elements suchas a transistor, diode, capacitor, resistor, semiconductor element(e.g., integrated circuits, hybrid integrated circuits, computer chips,and so forth), and so forth is not critical. Coating can be effectedwith the silicone compositions described previously.

The fabrication method of the present invention commences with primertreatment of the surface of cured silicone coated on an electricalelement such as those described above. Primer treatment can be byapplication of the primer described above by spraying, brushapplication, dipping, and so forth. The primer is preferably used inthis operation diluted with organic solvent or with organopolysiloxaneor alkoxysilane with a viscosity at 25° C. no greater than 50 mPa s. Theorganic solvent is exemplified by hydrocarbon solvents such as toluene,xylene, hexane, heptane, etc.; ketone solvents such as acetone, methylethyl ketone, etc.; alcohol solvents such as methyl alcohol, ethylalcohol, isopropyl alcohol, etc.; and also by chlorinated hydrocarbonsolvents and fluorinated hydrocarbon solvents.

Dilution with alkoxysilane or organopolysiloxane is particularlypreferred. The alkoxysilane is exemplified by methyltrimethoxysilane,vinyltrimethoxysilane, and so forth, while the organopolysiloxane isexemplified by straight-chain siloxanes such as hexamethyldisiloxane,trimethylsilyl-endblocked dimethylpolysiloxanes, and so forth, and bycyclic siloxanes such as octamethylcyclotetrasiloxane,tetramethyltetravinylcyclotetrasiloxane, and so forth.

The primer can then be dried, for example, by air-drying at ambienttemperature or by heating to no more than 200° C. as a function of theparticular requirements.

The primer-treated cured silicone is subsequently coated with the resinsealant described previously. The treated cured silicone can be coatedwith the resin sealant by, for example, transfer molding, injectionmolding, potting, casting, application by dipping, application bydripping as from a dispenser, spray coating, brush application, and soforth. To cure the resin, heat-curing resins can be heated to 50° C. to250° C.; UV-curing resins can be exposed to UV radiation from a lightsource; and moisture-curable resins can be held at room temperature. Theresin can be heated, for example, using an oven, hot plate, heat lamp,and the like.

Electrical components of the present invention have excellentreliability because the cured silicone coating the electrical element iswell bonded into a monolithic mass with the cured resin sealantover-coated on the cured silicone. The method of the present inventionfor fabricating these electrical components is highly productive andworkable.

EXAMPLES

So that those skilled in the art can understand and appreciate theinvention taught herein, the following examples are presented, it beingunderstood that these examples should not be used to limit the scope ofthe invention found in the claims.

The viscosity values reported in the examples were measured at 25° C.The following procedures were used to evaluate the adherence of thecured resin sealant to the cured silicone and to evaluate thereliability of the electrical components (semiconductor device,capacitor).

Synthesis of the Curable Silicone Composition

The following were mixed to homogeneity to give an additionreaction-curing silicone composition: 97.9 weight partsdimethylvinylsiloxy-endblocked dimethylpolysiloxane with a viscosity of400 mPa s, 2.0 weight parts trimethylsiloxy-endblockeddimethylsiloxane-methylhydrogensiloxane copolymer with a viscosity of 5mPa s, 0.1 weight part of a 1 weight % isopropyl alcohol solution ofchloroplatinic acid, and 0.01 weight part 3-phenyl-1-butyn-3-ol. Thiscurable silicone composition was used in the evaluations. Thiscomposition gave a silicone rubber with a JIS A durometer of 8 when thecomposition was cured by heating for 5 minutes in a forced convectionoven at 100° C.

Preparation of the Resin Sealant

The following were blended to homogeneity to give a curable epoxy resincomposition: 100 weight parts epoxy resin, with epoxy equivalent weightof 165, whose main component was a bisphenol F-type epoxy resin, 120weight parts tetraalkyltetrahydrophthalic anhydride curing agent withmolecular weight of 234, and 1 weight part 1-isobutyl-2-methylimidazolecure accelerator. This resin sealant was used in the evaluations.

Adherence by the Cured Resin Sealant to the Cured Silicone

The curable silicone composition described above was coated on analuminum plate and cured by heating for 5 minutes in a forced convectionoven at 100° C. The surface of the resulting cured silicone was thentreated with the primer by spraying followed by drying for 3 minutes inthe forced convention oven at 100° C. The resin sealant described abovewas coated on the resulting cured product and was itself cured byheating for 4 hours in the forced convection oven at 120° C. Theadherence of the cured resin sealant to the cured silicone was inspectedand scored on the following scale.

+: strong adherence

Δ: partial de-bonding

×: complete de-bonding

Electronic Component Reliability (Semiconductor Device)

The semiconductor device shown in FIG. 1 was fabricated as follows. Asemiconductor element 3 bearing an aluminum interconnect pattern on itssurface was mounted on an alumina ceramic circuit substrate 1 using anadhesive 2. The bonding pads 4 on the upper edges of this semiconductorelement 3 were then electrically connected to the circuit substrate 1using gold bonding wires 6. The curable silicone composition preparedabove was applied from a dispenser onto the surface of the semiconductorelement 3 and the cured silicone product 7 was then produced by heatingfor five minutes in a forced convection oven at 100° C. The surface ofthe cured product 7 was thereafter treated with the primer by sprayingand then drying by heating for 3 minutes in a forced convection oven at100° C. The above-specified resin sealant was then applied from adispenser onto the cured product 7. Due to the fluidity of this resinsealant, a rubber frame 10 (height=1 mm) had already been installedaround the periphery of the semiconductor element 3. Application of theresin sealant was followed by heating for four hours in a forcedconvection oven at 120° C. to fabricate a semiconductor device in whichcured resin sealant 9 was formed on cured silicone 7. Twentysemiconductor devices were fabricated using this procedure.

These semiconductor devices were subjected to thermal cycle testing (100cycles, 1 cycle =30 minutes at -30° C. and 30 minutes at +100° C.). Theoperating defect percentage was determined on the semiconductor devicesafter thermal cycle testing.

Electrical Component Reliability (Capacitor)

The capacitor shown in FIG. 2 was fabricated as follows.Al-vapor-deposited (metallized) polyester film 11 was rolled up,electrodes 12 were provided by coating both ends with flame-coatedmetal, and outer leads 13 were electrically connected to the electrodes12. This assembly was dipped in the curable silicone compositionspecified above and then heated for five minutes in a forced convectionoven at 100° C. to give the cured silicone 14. The surface of this curedproduct 14 was treated with primer by spraying and then drying for threeminutes in a forced convection oven at 100° C. The cured product 14 wasthen dipped in the resin sealant specified above followed by heating ina forced convection oven at 120° C. for four hours to give a capacitorwith cured resin sealant 16 formed on cured silicone 14. Twentycapacitors were fabricated using this procedure.

These capacitors were subjected to moisture resistance testingconsisting of standing for 1,000 hours in a 40° C./95% RH ambient. Theoperating defect percentage was determined on the capacitors aftermoisture resistance testing.

Reference Example 1

116 g 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, 100 g3-glycidoxypropyltrimethoxysilane, and 0.05 g potassium hydroxide wereintroduced into a four-neck flask equipped with a stirrer, thermometer,and reflux condenser. An equilibration polymerization was then run over3 hours while heating and stirring at 120° C. The reaction was thenstopped with dimethyldichlorosilane. The low boilers were eliminatedfrom the reaction mixture by vacuum distillation at 100° C./667 Pa toyield a liquid with a viscosity of 20 mPa s. Fourier transform nuclearmagnetic resonance analysis of this liquid confirmed it to beorganopolysiloxane with the following average unit formula. ##STR1##

Example 1

A primer was prepared by diluting 5 weight parts of theorganopolysiloxane synthesized in Reference Example 1 in 95 weight partstrimethylsiloxy-endblocked dimethylpolysiloxane with a viscosity of 0.6mPa s. This primer was used for evaluation of the adherence by the curedresin sealant to the cured silicone and evaluation of the electricalcomponent reliability (semiconductor device, capacitor). The resultsfrom the evaluations are reported in Table 1.

Example 2

A primer was prepared by diluting 2.5 weight parts silanol-endblockeddimethylpolysiloxane (viscosity=25 mPa s) and 2.5 weight parts3-glycidoxypropyltrimethoxysilane in 95 weight partstrimethylsiloxy-endblocked dimethylpolysiloxane with a viscosity of 0.6mPa s. This primer was used for evaluation of the adherence by the curedresin sealant to the cured silicone and evaluation of the electricalcomponent reliability (semiconductor device, capacitor). The resultsfrom the evaluations are reported in Table 1.

Comparative Example 1

The adherence by the cured resin sealant to the cured silicone and theelectrical component reliability (semiconductor device, capacitor) wereevaluated as in Example 1, but in this case omitting the primertreatment that was carried out in Example 1. The results from theevaluations are reported in Table 1.

Comparative Example 2

A dilution was prepared of 5 weight parts3-glycidoxypropyltrimethoxysilane in 95 weight partstrimethylsiloxy-endblocked dimethylpolysiloxane with a viscosity of 0.6mPa s. This dilution was submitted to evaluation of the adherence by thecured resin sealant to the cured silicone and evaluation of theelectrical component reliability (semiconductor device, capacitor). Theresults from the evaluations are reported in Table 1.

Comparative Example 3

A dilution was prepared of 5 weight parts silanol-endblockeddimethylpolysiloxane (viscosity=25 mPa s) in 95 weight partstrimethylsiloxy-endblocked dimethylpolysiloxane with a viscosity of 0.6mPa s. This dilution was submitted to evaluation of the adherence by thecured resin sealant to the cured silicone and evaluation of theelectrical component reliability (semiconductor device, capacitor). Theresults from the evaluations are reported in Table 1.

Comparative Example 4

The following were mixed to homogeneity to prepare an additionreaction-curing silicone composition to replace the curable siliconecomposition used in the evaluations: 97.9 weight partsdimethylvinylsiloxy-endblocked dimethylpolysiloxane with a viscosity of400 mPa s, 3.3 weight parts trimethylsiloxy-endblockeddimethylsiloxane-methylhydrogensiloxane copolymer with a viscosity of 5mPa s, 0.1 weight part of a 1 weight % solution of chloroplatinic acidin isopropyl alcohol, 2 weight parts of the organopolysiloxane preparedin Reference Example 1, and 0.01 weight part 3-phenyl-1-butyn-3-ol. Thisreplacement composition afforded silicone rubber with a JIS A durometerof 10 when cured for 5 minutes in a forced convection oven at 100° C.The adherence by the cured resin sealant to the cured silicone and theelectrical component reliability (semiconductor device, capacitor) werethen evaluated as in Example 1, but in this case using the replacementcomposition and omitting the primer treatment that was carried out inExample 1. The results from the evaluations are reported in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                                 comparative examples                                                present invention                                                                       Comp.                                                                              Comp.                                                                              Comp.                                                                              Comp.                                                Example 1                                                                          Example 2                                                                          Example 1                                                                          Example 2                                                                          Example 3                                                                          Example 4                         __________________________________________________________________________    adherence by the cured resin sealant to the                                                      +    +    ×                                                                            ×                                                                            Δ                                                                            Δ                           cured silicone                                                                semiconductor device reliability                                                                 0    0    15   15   5    10                                operating defect % after thermal cycle                                        testing                                                                       capacitor reliability                                                                            0    0    10    5   5     5                                operating defect % after moisture resistance                                  testing                                                                       __________________________________________________________________________

We claim:
 1. A primer for adhering a cured resin sealant to a curedsilicone coating on an electrical element, wherein the primer isselected from the group consisting of:(i) a mixture of components (a)and (b), (ii) a reaction mixture of components (a) and (b), (iii)component (c), (iv) component (c) and a mixture of components (a) and(b), and (v) component (c) and a reaction mixture of components (a) and(b),where component (a) is silanol-functional organopolysiloxane;component (b) is epoxy-functional organoalkoxysilane; and component (c)is organopolysiloxane with the average unit formula: (R¹ SiO_(3/2))_(a)(R² ₂ SiO_(2/2))_(b) (R² ₃ SiO_(1/2))_(c) (R³ O_(1/2))_(d) where R¹ isan epoxy-functional monovalent organic group; each R² is independently amonovalent hydrocarbon group, R³ is selected from the group consistingof hydrogen and alkyl groups of 1 to 4 carbon atoms; a, b, and d areeach a positive number; and c is 0 or a positive number.
 2. The primerof claim 1 wherein the silanol-functional polysiloxane (a) has astraight chain structure.
 3. The primer of claim 1 wherein component (a)is a silanol-endblocked organopolysiloxane selected from the groupconsisting of dimethylpolysiloxanes,dimethylsiloxane-methylvinylsiloxane copolymers, anddimethylsiloxane-methylphenylsiloxane copolymers.
 4. The primer of claim1 wherein component (b) has the general formula: R¹ Si(OR⁴)₃ where R¹represents an epoxy-functional monovalent organic group, and R⁴represents alkyl groups of 1 to 4 carbon atoms.
 5. The primer of claim 4wherein R¹ is a glycidoxyalkyl group.
 6. The primer of claim 4 whereinR⁴ is a methyl group.
 7. The primer of claim 4 wherein component (b) is3-glycidoxypropyltrimethoxysilane.
 8. The primer of claim 1 wherein thereaction mixture of components (a) and (b) is selected from the groupconsisting of condensation and equilibration reactions.
 9. The primer ofclaim 1 wherein the weight ratio of component (a) to component (b)ranges from 1:99 to 99:1.
 10. The primer of claim 1 wherein R¹ incomponent (c) is a glycidoxyalkyl group.
 11. The primer of claim 10wherein R¹ is 3-glycidoxypropyl group.
 12. The primer of claim 1 whereineach instance of R² in component (c) is independently selected from thegroup consisting of methyl, vinyl, and phenyl.